This invention relates to inkjet printing devices, and more particularly to an inkjet printing device that includes a printhead portion that receives drop activation signals for selectively ejecting ink.
Inkjet printing systems frequently make use of an inkjet printhead mounted to a carriage which is moved back and forth across print media such as paper. As the printhead is moved across the print media, a control device selectively activates each of a plurality of drop generators within the printhead to eject or deposit ink droplets onto the print media to form images and text characters. An ink supply that is either carried with the printhead or remote from the printhead provides ink for replenishing the plurality of drop generators.
Individual drop generators are selectively activated by the use of an activation signal that is provided by the printing system to the printhead. In the case of thermal inkjet printing, each drop generator is activated by passing an electric current through a resistive element such as a resistor. In response to the electric current the resistor produces heat, that in turn, heats ink in a vaporization chamber adjacent the resistor. Once the ink reaches vaporization, a rapidly expanding vapor front forces ink within the vaporization chamber through an adjacent orifice or nozzle. Ink droplets ejected from the nozzles are deposited on print media to accomplish printing.
The electric current is frequently provided to individual resistors or drop generators by a switching device such as a field effect transistor (FET). The switching device is activated by a control signal that is provided to the control terminal of the switching device. Once activated the switching device enables the electric current to pass to the selected resistor. The electric current or drive current provided to each resistor is sometimes referred to as a drive current signal. The control signal for selectively activating the switching device associated with each resistor is sometimes referred to as an address signal.
In one previously used arrangement, a switching transistor is connected in series with each resistor. When active, the switching transistor allows a drive current to pass through each of the resistor and switching transistor. The resistor and switching transistor together form a drop generator. A plurality of these drop generators are then arranged in a logical two-dimensional array of drop generators having rows and columns. Each column of drop generators in the array are connected to a different source of drive current and with each drop generator within each column connected in a parallel connection between the source of drive current for that column. Each row of drop generators within the array is connected to a different address signal with each drop generator within each row connected to a common source of address signals for that row of drop generators. In this manner, any individual drop generator within the two-dimensional array of drop generators can be individually activated by activating the address signal corresponding to the drop generator of row and providing drive current from the source of drive current associated with the drop generator column. In this manner, the number of electrical interconnects required for the printhead is greatly reduced over providing drive and control signals for each individual drop generator associated with the printhead.
While the row and column addressing scheme previously discussed is capable of being implemented in relatively simple and relatively inexpensive technology tending to reduce printhead manufacturing costs, this technique suffers from the disadvantage of requiring relatively large number of bond pads for printheads having large numbers of drop generators. For printheads having in excess of three hundred drop generators, a number of bond pads tends to become a limiting factor when attempting to minimize the die size.
Another technique that has been previously been used makes use of transferring activation information to the printhead in a serial format. This drop generator activation information is rearranged using shift registers so that the proper drop generators can be activated. This technique, while greatly reducing the number of electrical interconnects, tends to require various logic functions as well as static memory elements. Printheads having various logic functions and memory elements require suitable technologies such as CMOS technology and tend to require a constant power supply. Printheads formed using CMOS technology tend to be more costly to manufacture than printheads using NMOS technology. The CMOS manufacturing process is a more complex manufacturing process than the NMOS manufacturing process that requires more masking steps that tend to increase the costs of the printhead. In addition, the requirement of a constant power supply tends to increase the cost of the printing device that must supply this constant power supply voltage to the printhead.
There is an ever present need for inkjet printheads that have fewer electrical interconnects between the printhead and the printing device thereby tending to reduce the overall costs of the printing system as well as the printhead itself. These printheads should be capable of being manufactured using a relatively inexpensive manufacturing technology that allows the printheads to be manufactured using high volume manufacturing techniques and have relatively low manufacturing costs. These printheads should allow information to be transferred between the printing device and the printhead in a reliable manner thereby allowing high print quality as well as reliable operation. Finally, these printheads should be capable of supporting large numbers of drop generators to provide printing systems that are capable of providing high print rates.
One aspect of the present invention is an inkjet printing system that includes an inkjet printhead having a plurality of electrical contacts. The plurality of electrical contacts include address contacts and enable contacts for enabling drop generators and drive current contacts for providing drive current to enable drop generators for selectively ejecting ink therefrom. The printing system includes a printing device having a plurality of electrical contacts including address contacts, enable contacts and drive current contacts. The plurality of electrical contacts are configured to establish electrical contact with corresponding electrical contacts on the inkjet printhead upon insertion of the inkjet printhead into the printing device. The printing device provides periodic address signals and enable signals to the address and enable contacts one the printhead. In addition, the printing device selectively applies drive current to accomplish forming images on print media.
Another aspect of the present invention is an inkjet printhead responsive to enable and drive current signals for dispensing ink. The inkjet printhead includes an energy storage device for storing energy. Also included is an energy charging device responsive to a first enable signal for storing energy in the energy storage device. The inkjet printhead further includes an energy discharging device responsive to a second enable signal for discharging energy in the energy storage device. A drop generating device is included for dispensing ink from the inkjet printhead upon activation. The drop generating device is activated by a drive current signal active and energy stored in the energy storage device being greater than a threshold energy level.
Yet another aspect of the present invention is an inkjet printhead having a plurality of drop generators with each drop generator of the plurality of drop generators responsive to an activation signal and a drive current for selectively dispensing ink therefrom. The inkjet printhead includes a plurality of groups of drop generators for depositing ink on media Each of the plurality of groups of drop generators are capable of activation once over a printhead activation cycle. The printhead activation cycle is subdivided into a plurality of timeslots with each of the plurality of groups of drop generators having a corresponding timeslot associated therewith. The activation signal is active in the corresponding timeslot before drive current is provided. In addition, the activation signal is active for a duration that is less than a duration drive current is provided. Each drop generator within each group of drop generators is configured so that when activated the drop generator is active for the duration that drive current is provided.